In S. typhimurium that sites of mutations causing feedback resistance of anthranilate synthetase and phosphoribosyl transferase will be mapped in the first and second genes of the tryptophan operon. The mutations will be relating to the structural alterations in the enzymes by "fingerprinting" peptide fragments. The basis for suppression of promoter mutations and stimulation of nonmutant operons by supX mutations will be studied by in vitro protein and mRNA synthesizing systems, by the in vivo maxicell system, by study of the structures of the mutant promoters, by the interactions with regulatory mutations, and by examination of the subunit structure and function of RNA polymerase. The mechanisms for unstable initiation of gene expression will be studied by genetic mapping techniques and factors affecting the formation and excision of tandem chromosomal duplications will be analyzed. The basis for the specificity of interaction between the phage encapsulating mechanism and the substrate DNA will be analyzed by means of the phage mutations which modify the formation of transducing DNA fragments.